How do you know if it's time to rebuild the carb?

[UNSUREBOATGUY]

Hello gents,

I'm sorry if this has been covered. 1987 Mercruiser 3.0 Alpha 1 with the Mercarb # 1389-9562. The engine starts fine cold, idles well once warmed up and runs well up to WOT on the lake with no problem. Occasionally there is some hesitation when I hit the throttle hard from a dead start (starting a tuber or skier). It seems as though as long as I move the throttle smoothly and quickly, but not like slamming the accelerator down, it accelerates fine.

The other issue is that it is a little difficult to start after shutting down to switch tubers, or stop to swim for a while (difficult warm start). It's not terrible, but it seems like it should start easier. I seem to have the best luck with the lever at 1/4 to 1/2 (throttle only), but it typically takes a fair amount of cranking, or two tries to get it to fire up. I don't want to crank too long-don't want to over heat the starter. I've tried pumping the throttle once, less throttle, more throttle, etc.-just seems like it should be easier.

Granted I'm 36 and don't have that much experience with carbed engines, so I am spoiled by cars/trucks that start with just a turn of the key. I'm not sure if the carb has ever been rebuilt as it still has it's nice shiny black paint. Is it reasonable to think that the carb might be leaking at shutdown, flooding the engine a little and making it harder to start? Maybe a new accel pump will help with the slight hesitation at takeoff?

What I'm asking is-should I rebuild the carb? I was planning to get the dip, soak it and blow out everything with compressed air (following the Merc manual) and get the kit (18-7098-1) and float (18-7202). Is it worth the hassle, or is it already performing the way it should for a boat that age? And are these the right parts? Sorry so many questions.

Thanks a ton for your time helping out a guy who doesn't know much about carbs.

 

[ktbarrentine]

Re: How do you know if it's time to rebuild the carb?

Two suggestions to pursue: 1. Have you checked for fuel in your sight-flow tube from the fuel pump to the carb air-horn? I had your exact same symptoms and traced it down to a cracked diaphram in the fuel pump, putting excess gas into the carb. Sight flow tube should always be dry.
2. Have you checked your choke for proper operation. If it is closed too far, or stuck, it will affect warm starting.
Two easy things to check before tearing into the carb....Which I find fun to do anyways... especially for a carb that age.

 

[Oshkosh1]

Re: How do you know if it's time to rebuild the carb?

Look down the throat right after you shut it off. If you see fuel dripping it could be the sign of either a bad needle seal, or a bad float. Rebuilding the carb is not a difficult process at all. When/if you do rebuild it, get a new brass float.

 

[fat fanny]

Re: How do you know if it's time to rebuild the carb?

It's a carburator don't expect mirracles they do have hessitations on take off from time to time. Try the above said looking down the the carbs air horn when shut down after a run to see if it's dripping. If it is starting hard after a stop try letting it run at idle in neutral before shutting down to burn off any excess fuel in carb this will help prevent hard starts. If you do decide to re-build it it;s a 50/50 shot at success but a good thourough cleaning helps chnaces of success dissasemble,wash all parts in warm soapy water,blow out with compressed air, soak all parts in carb cleaner over night(except plastic) blow out with compressed air probe all orafices with tip cleaner or small wire, re-wash with warm soapy water, blow out with compressed air and resoak in dip over night and blow out with compressed air re-assemble with new kit have a neat and orginzed work area that is well lit and follow the instructions to a T another tip is to smear vasoline on both sides of all the gaskets it helps if you have to dissasemble for a float adjustment later prevents tearing. good luck and post back!

 

[RCAnderson]

Re: How do you know if it's time to rebuild the carb?

It sounds to me like your accelerator pump may not be doing it's job, and that your idle circuit is not functioning correctly, and possibly your float setting is not correct. A carb rebuild is certainly not rocket science, and can make a world of difference. There should be no hesitation on acceleration, that's what the accelerator pump is for, and as for starting while warm, it's either an idle air issue or a float issue or you are boiling the gas out of you float bowl. I would rebuild the carb, making sure to replace the float, as many carb kits don't come with one.

 

[888]

Re: How do you know if it's time to rebuild the carb?

It sounds to me like your accelerator pump. I would rebuild the carb, making sure to replace the float, as many carb kits don't come with one.

Yuup...Sounds like it to me too.. If accelerator pump isn't working its "Time to rebuild". There shouldn't be any hesitation if working properly.Make sure you replace your float with brass.

 

[Oshkosh1]

Re: How do you know if it's time to rebuild the carb?

or you are boiling the gas out of you float bowl.

If the carb is "hot" this is a real problem as it will act as a heat sink. I installed a 1/2" phenolic spacer between mine and the manifold. Cooled it down considerably. Easy install...just needed to buy longer studs.

 

[keith2k455]

Re: How do you know if it's time to rebuild the carb?

It sounds to me like your accelerator pump may not be doing it's job, and that your idle circuit is not functioning correctly, and possibly your float setting is not correct. A carb rebuild is certainly not rocket science, and can make a world of difference. There should be no hesitation on acceleration, that's what the accelerator pump is for, and as for starting while warm, it's either an idle air issue or a float issue or you are boiling the gas out of you float bowl. I would rebuild the carb, making sure to replace the float, as many carb kits don't come with one.

fully agree

 

[nola mike]

Re: How do you know if it's time to rebuild the carb?

Disagree on this one. A bad ap makes it sputter and die on acceleration, but from a dead stop it isn't unusual for a carbed engine to hesitate if you slam it. Sounds like the warm start might be more of an issue, but again, you'll need to have your throttle open normally on a warm start.

 

[havoc_squad]

Re: How do you know if it's time to rebuild the carb?

Hard starting shortly after a shutdown (5 minutes or less) with the engine fully warmed up makes me to believe most likely a slight flooding condition after shutdown.

Flooding issue can be checked by watching the venturies and seeing if they drip any during idle or after engine shutdown.


However, hard starting after 10 minutes or longer while the engine warm after moving the throttle 1/3 to 1/2 and keeping it there makes me believe your accelerator pump is probably not putting enough fuel into the intake.

If you're accelerator pump is not discharging enough fuel into the intake, warm starts are difficult because the engine doesn't have enough fuel to motivate it to start when the throttle is opened up.

Easy way to check this, is have the carb intake visible of you looking with the engine off, then move the throttle to wide open. You should see two powerful streams of fuel squirt out.

 

[UNSUREBOATGUY]

Re: How do you know if it's time to rebuild the carb?

Thanks a ton for all of the input guys. Might be a good project for over the winter. Any suggestions as to where to find the brass float?

 

[ktbarrentine]

Re: How do you know if it's time to rebuild the carb?

Thanks a ton for all of the input guys. Might be a good project for over the winter. Any suggestions as to where to find the brass float?

Here's one source: http://www.amazon.com/CARBURETOR-FL...F8&qid=1347808508&sr=8-1&keywords=77230+float

Part number 77230


Here's a good chart:

http://www.sterndrive.info/sterndriveparts/carburetor_kit.html

 

[havoc_squad]

Re: How do you know if it's time to rebuild the carb?

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